Arena actually gave freedom through it's roleplaying restrictions, in that you didn't have all the stats to worry about as long as you played your specified role.
Battlespire, while not innovative in it's skills, actually made skills work and brought things back to brass tacks. critical damage actually did critical damage. stabs that were parried stunned you. there were many gameplay things that just clicked in battlespire.
Morrowind had the most thought out classes and skills of all the games, refining everything daggerfall did and made it much more playable, while being a bonafide RPG.
Oblivion went back to the heart of elder scrolls started in arena, and took some of the lessons from morrowind and melded them to be stat based but organic elements of gameplay.
Skyrim let you be whatever you wanted to be, but made you think about your skill progression in terms of how you actually play the game, how you play the role, vs titles or restrictions.
Given thought from then to now, we can learn from the games and make skills actually mean something, but keep the feel and appeal of daggerfall. it can be redone.
Revamping Skills & Classes